(1) Field of the Invention
The present invention relates to an axially retained wide flexing angle homokinetic joint.
It deals more particularly with a homokinetic joint of the type comprising a tripod-shaped element connected to one of two shafts to be coupled, and a tulip element connected to the other of the shafts, the tripod element comprising three trunnions on which are rotatively and slidably mounted rollers received in three rolling tracks provided in the tulip element, and axial retaining means for maintaining the two parts of the joint in position relative to each another.
(2) State of the Prior Art
Homokinetic joints, known as fixed tripod joints, have been used for many years in the automotive industry, in which they are installed at the wheel end of transmission systems transmitting the drive from the power unit to the driving wheels of front wheel drive vehicles. The design principle of homokinetic joints of this type has been described and illustrated in the document FR-A-1,272,530.
Minimum dimensions, with respect to both diameter and length, and the widest possible angle of flexure, are the two main requirements due to the use of these joints in motor vehicles of recent design.
A homokinetic joint in which the rolling tracks are of a substantially toroidal shape and receive the rollers, whose outer surface is spherical, has small longitudinal dimensions and also a slightly smaller diameter than a joint in which the roller tracks have their axes parallel to the axis of the tulip element. In addition, the tulip connected to one of the two shafts to be coupled and the bowl-shaped member which serves to connect the tripod element to the other shaft can penetrate one into the other, as in the case of the jaws of a wide-angle cardan joint. A basic arrangement of this kind is known from the document U.S. 3,877,251, but it provides only a partial solution to the problem of a very wide-angle joint of small dimensions.
In order to eliminate the relative axial freedom of movement of the two shafts, it is necessary to provide an appropriate device which enables the homokinetic joint to keep its properties of mechanical strength and angular movement. Thus, in the document FR-A-1,272,530 the basic principle adopted there (FIGS. 3 and 8) consists in giving the central part of the tripod element a spherical shape cooperating with two opposite plane surfaces extending in substantially radial plane and provided in the tulip element. Nevertheless, in an arrangement of this kind the application of the axial stresses is practically punctiform and the joint wears out relatively rapidly.
Subsequently, numerous solutions were proposed for axially retained tripod of similar joints, for example those described in the document FR-A-2,398,924, which employ the principle consisting in axially maintaining the joint through the cooperation of plane surfaces and spherical dome-shaped segments in the proximity of the axis of rotation of the second shaft.
However, the document FR-A-2,398,924 describes, and illustrates in FIGS. 7 to 11, a homokinetic joint in which the axis of the rolling tracks is parallel to the shaft connected to the tulip element, but in which the axial retainer comprises an intermediate member delimiting a convex spherical outer surface received in a concave spherical cavity entirely formed in the tulip element. Although it enables the joint function characteristics to be substantially improved, this design has the main disadvantage of entailing large dimensions of the joint both with respect to diameter and with respect to length, while, in addition, its maximum flexing angle is substantially equal to 43.degree..
The kinematics of the joint must also permit displacements of the tripod element in a plane defining a right angle to its axis, which is impossible in the case of the joint described in the document U.S. 3,877,251, which does not appear to be able to allow the joint to be placed at an angle without jamming. Moreover, the design of this joint is scarcely realistic from the point of view of large scale industrial production.
Also known in the document FR-A-2,394,711, which desribes and illustrates a transmission joint which does not belong to the technical domain of axially retained joints, since it is a joint permitting axial sliding of one shaft relative to the other. The structure of the components ensuring the connection between the tripod element 104 and the tulip element does not allow movement of the tripod element in a plane at right angle to its axis for the purpose of absorbing the offset movement. Quite on the contrary, as is indicated in Page 1 (lines 22-25) of document FR-A-2,394,711, the aim sought is to suppress the offset movement of the shaft connected to the tripod element.